I'm an ex-mechanic myself and love taking stuff to bits as I work on the principle that if they put it together then it'll come apart
Sad but I find it all very therapeutic
I've rebuilt my laptop, PS4, American fridge-freezer, boiler (no, not the wife...the other one) and other various items that 3 kids generally destroy
I'd place the engine in a position to allow you to pour some diesel into the bores/chambers and leave them to soak for a good while
This'll hopefully penetrate in and around the piston rings and skirts of the pistons so you'll minimise any damage to themselves and bores.
If it free's up you'll get away with a hone of the bores without the need of a re-bore and new pistons costing you money.
Paul




